Various signal processing techniques have been proposed to design transmit beamformers for multi-antenna BS and MIMO radar to realize efficient interference management. A null space projection (NSP) method was proposed in [1]}, [2]}, where the radar transmit beamforming is designed to project the radar signals onto the null space of the effective interference channels to eliminate the interference at the communication receivers.
However, the target echo may fall into the row space of the interference channels, resulting in degraded radar performance.
As a step further, the authors of [3]} expanded the projection space to include the subspace corresponding to the small non-zero singular values under a specified threshold, expecting to control the interference to communication systems and achieve different trade-offs between radar and communication performance.
However, these NSP-based beamforming designs significantly reduce the DoFs for optimization and cannot guarantee to meet specific radar sensing requirements.
In order to overcome these disadvantages, investigations on the joint design of the transmit beamformers for both radar and communication systems have been proposed in [4]}, [5]}, where different performance metrics of these two systems are satisfied with controllable constraints.
In addition to the above scenarios with perfectly known channel state information (CSI), a robust beamforming design was proposed in [6]} under the assumption of imperfect CSI.
